The present invention relates to a method for aligning electronic components, and more particularly to a method of aligning an electronic component with a printed board in which the position of a conductor pattern on the printed board and the position of each lead of the electronic component are detected by optical means.
In a typical one of the conventional methods for aligning a chip-mounted component with a printed board, the printed board is irradiated with light to form an image of a conductor pattern on the printed board by reflected light from the printed board, the component is also irradiated with light to form an image of the component by reflected light from the component, and the positional deviation of one of these images from the other image is detected to correct the position of the printed board on the basis of the deviation.
An example of conventional component alignment apparatuses for carrying out the typical method will be described below. A printed board is placed on an XY-table which is movable on a horizontal plane, and then irradiated with light. The reflected light from the printed board is led to a television camera so that an image of a conductor pattern on the printed board is formed on the television camera by the reflected light and is detected by the television camera. Next, a chip-mounted component which is to be aligned with the corresponding conductor pattern, is disposed above the printed board and coarsely aligned with the printed board. Then, the component is irradiated with light, and the television camera is moved to an appropriate position so that an image of leads of the component is formed on the television camera by the reflected light from the leads. The amounts of positional deviation of the image of the leads from the image of the conductor pattern in X- and Y-directions are determined by an appropriate processor, and the XY-table is moved so that the determined positional deviation is corrected, that is, the leads of the component are accurately located in relation to the conductor pattern on the printed board.
However, a method of this kind which utilizes the reflected light from a conductor pattern as in the case of the above-mentioned component alignment apparatus involves a substantial disadvantage. Namely, where the conductor pattern is a solder pattern, the surface condition is not uniform, and there are variations in surface condition among individual samples of the conductor pattern. In other words, there is a disadvantage that since there are variations in shape, surface luster, etc., among the different samples, the reflected light from the conductor pattern is not stable and the binarization of a video signal with respect to the conductor pattern is not an easy matter. There is another problem that depending upon a manner in which the printed board is irradiated with light, the surface of the printed board gleams thus making it difficult to distinguish the conductor pattern from the substrate of the printed board.
The present invention has been made on the basis of an idea of utilizing fluorescent light emitted from the substrate of a printed board, which occurred in the course of an investigation into any other method than the method of utilizing the reflected light from a conductor pattern.